Surgeons and surgical assistants have been using medical devices incorporating radio frequency (RF) electricity for many years to cauterize and coagulate bodily tissues during surgical procedures. Two types of RF surgical devices are conventionally utilized: mono-polar and bipolar. Both incorporate a pair of conductors for transmission of alternating RF electricity. In a mono-polar electrosurgical instrument, a first conducting electrode having a first polarity is typically placed on the patient's skin and communicates through the body, i.e. forms a conductive path, with a second conducting electrode having the opposite polarity located on the surgical instrument. A bipolar electrosurgical instrument, however, typically incorporates both first and second electrodes of opposite polarity in the same surgical instrument, substantially restricting the flow path of electric current to tissue that is contained between the electrodes. As mentioned previously, both mono-polar and bipolar electrosurgical instruments apply RF energy through tissue. The energy is dissipated within the tissue in the form of heat due to the natural impedance of tissue. As the temperature of the tissue rises, the electrical resistivity of the tissue increases. When RF energy is applied to tissue, and as the temperature reaches about 67-70 degrees Celsius, the tissue begins to coagulate. As increasing amounts of energy dissipate in the tissue, the collagen forming the tissue matrix breaks down and appears to “melt”. Mechanical compression of the coagulating tissue layers fuses and seals any contained blood vessels, so that the tissue may be cut without bleeding. When the tissue temperature reaches 100 degrees C., most fluids (including water) vaporize into the surrounding tissues and air.
The energy dissipation rate in tissue depends on numerous factors, including the inherent electrical resistivity of the tissue and the electrical current density. Electrical current density in various tissues is an important consideration in the design of the electrodes in a bipolar electrosurgical instrument, including the number, size, shape, and placement of the electrodes.
Many surgeons prefer to use bipolar electrosurgical instruments for hemostatically (without bleeding) sealing tissue prior to transection. Bipolar electrosurgical devices are known for grasping, coagulating, and cutting tissue. Typically the instruments have grasping elements, and one of the grasping elements is an electrically opposite pole of the other grasping element. For this type of conventional, bipolar electrical configuration, electrical current can be simplistically thought of as “flowing” from one grasping element (a positive pole), through the grasped tissue, and to the other grasping element (a negative pole). When tissue held between the grasping elements is coagulated, it is known that the electrical resistivity of that portion or zone of tissue increases dramatically. This causes the electrical current to seek a new path of lesser electrical resistivity around the zone, resulting in a spread to tissue adjacent to the outside of the grasping elements. Accordingly, it is believed that the zone of coagulated tissue continues to increase laterally from the grasping elements. The final width of the coagulation zone depends on several factors, including the power setting of the electrosurgical generator, and on the length of time the operator applied electrical energy to the tissue, etc. It is typical for an operator to apply electrical energy (usually by stepping on a foot actuator) for several seconds more than is actually needed to ensure that the grasped tissue is completely coagulated prior to cutting to prevent bleeding. If the amount of tissue grasped is very small, coagulation of the grasped tissue may occur so quickly that the operator cannot stop the application of electrical energy quickly enough to prevent excessive lateral spreading of the coagulation zone. In addition, the operator may not always be able to visualize the spreading of the coagulation zone because of obstructing tissue structures, especially during an endoscopic procedure; or, because the coagulation of the tissue occurs on the inside of the tissue or blood vessel.
Excessive lateral spread of the coagulation zone may be harmful to patients undergoing surgical procedures in which an organ or vessel is harvested for use in the same or a different patient. For example, in a coronary artery bypass graft (CABG) procedure, a surgeon or surgical assistant may remove a saphenous vein from one of the patient's legs to use as one or more bypass grafts on that patient's heart. In recent years, new surgical dissecting/retracting tools have been introduced to enable the surgical operator to harvest the saphenous vein endoscopically. Examples of endoscopic vessel harvesting devices and methods are contained in the following U.S. Patents, which are incorporated by reference: U.S. Pat. Nos. 5,667,480; 5,722,934; 5,928,135 and 5,928,138. In such surgical procedures the operator “tunnels” with the surgical dissecting/retracting tool alongside the vein under the skin, working through a small incision made into the inside of the patient's leg or knee. The benefits of this procedure to the patient are numerous because endoscopic vein harvesting (EVH) results in greatly reduced recovery time and pain for the patient as compared to the earlier open procedure of creating an incision along the leg equal to the length of the vein harvested. In addition scarring is limited, and the incidence of serious infections reduced.
In conventional EVH procedures, the surgical operator uses the surgical dissecting/retracting tool to create a small working space at the distal end of the tool and adjacent to the vein being harvested. As the operator maneuvers the tool along the vein to separate the vein from adjacent tissues, the operator typically encounters numerous smaller collateral vascular side branches of the main vein (usually about 15). To harvest the main vein with minimal bleeding of surrounding tissues, the operator may apply at least two conventional surgical clips to each side branch encountered, using a conventional mechanical endoscopic surgical clip applier. Then the clip applier is removed, an endoscopic scissors is inserted to cut the side branch between the applied clips. Each instrument insertion and removal is not only time-consuming, but care must be taken not to cause trauma to the vein being harvested and to surrounding tissues in the leg. The operator may also use bipolar electrosurgical scissors in place of mechanical clip appliers, which are well known in the art for use in this type of surgical procedure. However, bipolar scissors may induce undesirable lateral spreading of the coagulation zone if not used correctly, and the experience of the operator is crucial in preventing injury to a harvested vein to be used in the CABG procedure. When using bipolar scissors or any of the other conventional electrosurgical instruments during an EVH procedure, the operator is required to treat each side branch at a location as far distant laterally from the main vein as practical, and the operator must apply RF energy for a minimal time to seal the side branch for cutting.
Various embodiments of a relatively new kind of bipolar, electrosurgical device are disclosed in the following patents hereinafter referred to collectively as the “offset electrode device”, and are incorporated by reference herein: U.S. Pat. Nos. 5,403,312; 5,709,680; and 5,833,690. In the offset electrode device, the bipolar electrodes have an “offset” configuration and coagulation of tissue is substantially confined to only the tissue held between a pair of interfacing surfaces. The offset electrode devices also provide for high tissue compression to coagulate tissue uniformly and to force fluid out of the coagulation zone. Such fluid would vaporize during coagulation and shoot laterally from the interfacing surfaces, possibly causing thermal injury to adjoining tissue. The offset electrode devices disclosed, however, in the referenced patents are not specifically adapted for use in endoscopic vein harvest procedures or in other types of minimally invasive surgical procedures requiring 5 mm diameter endoscopic ports. There is a need in this art for a bipolar electrosurgical instrument that may be used through a five-millimeter trocar port, and that has minimally sized jaws for improved access and visualization of tissue structures in the surgical site.
Another concern of the surgical operator when using any electrosurgical instrument is the tendency of coagulated tissue to stick to the jaws of the instrument during operation of the instrument. The operator must take additional time to manipulate the instrument to release tissue adhering to the end effectors, possibly injuring surrounding tissue, especially when operating in limited working spaces during endoscopic procedures. Adhering tissue also reduces the electrical conductivity of the bipolar electrodes and it is often necessary for the operator to manually clean the electrodes in order to continue using the instrument. This is especially prevalent for forceps-type grasping instruments incorporating the conventional bipolar electrode (non-offset) configuration.
Many conventional surgical instruments incorporate cutting blades for transecting tissue held within the jaws. A potential difficulty with cutting blades of such instruments is “tissue-tagging” when the blade does not completely cut through all the tissue held in the jaws. This may occur, for example, if the cutting edge of the blade is dull or nicked. Another reason tissue-tagging may occur, or even some bleeding after the tissue is coagulated and cut, is that the tissue is not held firmly enough within the jaws of the instrument as the cutting blade is passed through the tissue held. When tissue is initially clamped within the jaws of the instrument, the clamping force may be very high due to the elasticity of the fluid-containing tissue. But after the tissue has been compressed for a period of time, and then is coagulated, most of the fluid has been driven out of the tissue, with the result that the elasticity of the tissue is greatly reduced. The clamping force on the tissue is also decreased so that the tissue may shift within the jaws as a cutting blade is passed through it. This presents the possibility that not all the tissue will be cut, or the cutting blade will pass through a portion of tissue that is not fully coagulated.
During some surgical procedures, including the EVH procedure, the surgical operator must cut and dissect a first tissue structure away from a second tissue structure prior to performing a transection or other surgical procedure on the second tissue structure. A conventional technique for this type of surgical cutting and dissecting used a pair of conventional, mechanical scissors held in an open configuration, thus forming a vee-shape with the scissors blades. The scissors blades are then advanced between the first and second tissue structures to cut and separate them. At this point, the surgical operator may remove the scissors and continue the surgical procedure with another surgical instrument such as a clip applier for ligation of the second tissue structure. During an EVH procedure, the exchange of endoscopic mechanical scissors and the clip applier in and out of the working space may occur many times, increasing the time to perform the procedure, and possibly injuring the vein or surrounding tissue. An alternative to using a mechanical scissors together with a clip applier is to use a bipolar electrosurgical scissors as described previously. Using conventional bipolar coagulation and cutting devices may result in excessive lateral spreading of the thermally affected zone of tissue, especially if the operator is inexperienced or otherwise not careful.
Another shortcoming when using currently available electrosurgical cutting instruments with cutting blades is that the cutting blade may be exposed accidentally to adjacent tissue when the operator does not intend to cut the tissue.
Accordingly, what is needed in this art is a bipolar electrosurgical instrument incorporating offset electrodes and compression zones, as described for the offset electrode device, yet improved to be less surgically invasive and to provide better access and visualization at the surgical site. There is also a need for a bipolar electrosurgical instrument that easily releases tissue from the jaws after each cycle of use, and automatically wipes electrode surfaces clean for each cycle of use. Additionally, there is a need for an instrument having more than one cutting blade that cuts through the tissue held within the jaws to improve the probability of completely transecting the tissue held, but without increasing the size or cost of the instrument. There is also a need for an instrument that provides for additional clamping force to be applied to tissue held in the jaws immediately prior to passing a cutting blade through the tissue. There is yet a further need for an instrument that safely coagulates tissue without excessive lateral thermal spread, and which reduces the need for using mechanical scissors and clip appliers during a surgical procedure. Replacing a scissors and a clip applier with a single bipolar electrosurgical cutting instrument, for example, and reducing surgery time by reducing the number of instrument exchanges during the surgical procedure, allows a significant cost savings to the hospital, and is beneficial to the patient. There is also a need for an electrosurgical instrument with a cutting blade that has an operational sequencing element that allows the movement of the cutting blade through a tissue grasping region only when the jaws are fully closed, thus reducing the possibility of accidentally injuring the patient.